1. Field of the Invention
The present invention relates to a carboxylic acid-modified nitrile copolymer latex (hereinafter also referred to as a ‘copolymer latex’) for the production of a molded article that does not undergo long stirring and maturation, causes no allergic reactions due to the absence of sulfur and a vulcanization accelerator, has good oil resistance and high mechanical strength, and produces a soft feeling. The present invention also relates to a latex composition for dip forming comprising the copolymer latex, and an article produced from the latex composition by dip forming.
2. Description of the Related Art
Rubber gloves are currently used in a variety of applications, including food, electronic and medical industries, as well as household applications. Most rubber gloves have been produced from natural rubber latexes by dip forming. However, proteins contained in natural rubber cause allergic reactions such as pain and rash in some sensitive users.
Under such circumstances, many efforts have been made to produce gloves from synthetic rubber latexes that cause no allergic reactions. For example, gloves are produced by blending a carboxylic acid-modified nitrile copolymer latex (e.g., an acrylic acid-acrylonitrile-butadiene copolymer latex), sulfur and a vulcanization accelerator to prepare a latex composition, and dip forming the latex composition.
However, the latex composition should undergo stirring and maturation for a long time, typically at least 24 hours. This long stirring and maturation results in low productivity of the gloves.
Further, when a wearer of rubber gloves produced from a composition essentially comprising sulfur and a vulcanization accelerator works for a long period of time, he/she may experience allergic reactions such as skin irritation. Further, the sulfur produces an offensive smell, making him/her unpleasant, and the gloves tend to discolor over time, resulting in loss of their commercial value.
Japanese Unexamined Patent Publication No. 2006-321955 discloses a latex composition for dip forming comprising a conjugated diene rubber latex and an organic peroxide without using sulfur and a vulcanization accelerator, and an article produced from the latex composition by dip forming. The use of the latex composition eliminates the need for long stirring and maturation in the production of the dip-formed article. Further, the dip-formed article undergoes no discoloration even after long-term use. However, a solution of the organic peroxide is harmful to humans and poses a danger of fire or exploration when heat or impact is applied thereto.
U.S. Pat. No. 7,345,111 discloses a glove that is produced using an acrylic emulsion latex and a monomer crosslinkable with the acrylic emulsion latex without the need for long stirring and maturation. The acrylic glove causes no allergic reactions due to the absence of sulfur and a vulcanization accelerator, but it has the problem of high sensitivity to temperature.